Time-limit relay



G. A. BURNHAM.

TIME LIMIT RELAY.

APPLICATION FILED MAY 26. 1917.

1 ,357 ,68 1 Patented Nov. 2, 1920.

Ja e/1702, $6. A M

WJDI' UNITED STATES PATENT OFFICE.

GEORGE A. BURNHAM, OF SAUGUS, MASSACHUSETTS, ASSIGNOR TO SEARS B. CONDIT, JR., 0]? BROOKLINE, MASSACHUSETTS.

TIME-LIMIT RELAY.

Application filed May 26, 1917.

To all whom it may concern Be it known that I, GEORGE A. BURNHAM, a citizen of the United States, residing at Saugus, in the county of Essex and State of Massachusetts, have invented an Improvement in Time-Limit Relays, of which the following is a specification.

My invention relates to that type of time limit relay in which an overload in the line which the relay is designed to protect serves to rotate the armature of an electromotor, which operates to move an arm into position to control an electric circuit to cause the opening of the line switch.

In the operation of this type of relay, the time intervening between the occurrence of an overload and the opening of the line switch is usually inversely proportional to the strength of the overload, and with say a 100% increase of overload, the time interval will drop 300 to 400%, or in other words, the time interval, "with overloads of from two to three times normal overload, is much shorter than is desirable. It is quite desirable to obtain a relay in which the time interval is inversely proportional to the strength of the overload up to a certain 'predetermined overload, and, for overloads above that point, to have the relay maintain a practically constant time interval, and consequently the object of my invention is to provide means whereby the relay may operate in the manner specified.

Briefly, I accomplish this result by compensating for the increased driving torque set up in the armature of the time limit relay by the increased overload in providing an increased resistance against rotation of the armature, which resistance is maintained practically proportional to the increased driving torque, whereby a practically constant angular velocity is maintained by the armature, regardless of the strength of the overload. The mechanism-by which this result is obtained is in the provision of a permanent or damping magnet," the poles of which are disposed on each side of the disk or armature, and which is pivoted about an axis and adapted to be moved from a position near the center of the disk to a position toward the periphery of the disk under control of an electromagnet ener ized as a function of the overload, Where y the greater rate of flux cutting by the disk sets up an Specification of Letters Patent.

Patented Nov. 2, 1920.

Serial No. 171,275.

stant rate of angular velocity of the disk or I armature. Figure 1 illustrates an embodiment of my invention as applied to a time limit relay.

Armature or disk 5 bears an arm 6 which is adapted to engage with contact member 7 in the greatest displaced position of disk 5. Disk 5 is maintained in normal position with arm 6 against a stop 8 by a spring 9 attached to shaft 10 of disk 5.

An energizing or driving magnet 11 has its poles disposed on each side of disk 5 and in its pole faces are shading coils 12, which serve, upon energization of magnet 11 by an alternating flux, to set up a drivin torque in disk 5. Magnet 11 is provide with a coil or winding 13 adapted to be energized in proportion to the overload.

The relay as above described is of common construction.

A permanent or damping magnet 14 with its pole faces disposed upon opposite sides of disk 5 is secured to a lever 15, which is pivotally mounted at 16, and which bears, at its opposite end, an armature 17 of electromagnet 18. A spring 19, adjustable for tension by means of thumb nut 20, serves to normally maintain lever 15 againsta stop 21 with damping magnet 14 near the center of disk 5. As lever 15 is moved away from stop 21, upon eflective energization of electromagnet 18 and against the action of spring 19, the magnet 14 is moved toward the periphery of disk 5, and, with a given angular velocity of disk 5, the rate at which the magnetic flux of damping magnet 14, is

cut by disk 5 in the displaced position of cientlyenergized to create. sufficient torque I to rotate 29 and of which are in series with the line wires 31 and 32.

the current flowing in coils 13 and 22 will always bear some substantially constant ratio to the line current.

Arm 6 attached to disk 5, and contact ,member 7 serve to control an electric circuit from a current source 33 through a trip coil 34 of a switch 35 interposed in series with line wires 31 and 32 and the power consuming device 36 to open switch 35 at some time interval after the occurrence of an overload.

With a normal current flow in line 31-32, magnet 11 is arranged to be insuffidisk 5 against the retractile effort of spring 9' away from its normal position against stop 8, and magnet 18 is arranged to be insufliciently energized to move'lever 15 away from stop 21 to displace damping magnet 14 from its normal position near the center of disk 5. I

Upon the occurrence ofa normal overload, the torque set up between energizing magnet 11 and disk 5 is sufficient to impart rotation to disk 5 which consequently rotates to carry arm 6 into contact with member 7,

"whereby a circuit may be established from current source33 to trip coil 34 of switch 35 and the switch 35 opened. Due to the consequent cessation of the overload and therefore the driving torque, disk 5 returns to its normal inoperative position. The energization of magnet 18 has been insuflicient during this normal overload to cause the displacement of damping, magnet 14.

With any increase of overload, below that at which magnet 18 is designed to become sufiiciently energized to cause a displacement of. damping magnet 14, the driving torque created between disk 5 and energizing mag- I net 11 will increase as a function of the 1ncrease of overload and consequently the time intervening between the occurrence of the overload and the subsequent opening of switch 35 will be an inverse function of the strength of the overload.

Upon an overload in excess of the predetermined value, magnet 18 becomes sufficiently energized to attract its armature 17 of lever 15 against the tensile force of spring and consequently displaces damping magnet 14 a certain distance toward the periphery of disk 5. The proportional displacement of magnet 14 may be made any desired amount by the proper design of the mechanism and by the adjustment of spring 19. V

In the displaced position of damping magnet 14 toward the periphery of disk 5, the rate athich the flux of magnet 14 is cut by disk 5 is proportional to the displacement of magnet 14 and consequently the resistance against rotation is proportionally increased.

Sincethe electromagnet 18, controlling the position of damping magnet 14, and the en-- ergizing or-driv'ing magnet '11 are arranged 70.

,to be equally energized byan overload, it is seenthat by proper design and arrangement of the mechanism the resistance to rotation ofdisk 5, caused by damping magnet 14, may be made substantially equal to the driving torque set up in disk 5 bymagnet 11 by an overload, and therefore the rate of angular movement of said disk may be made substantially independent of the amount of overload, for current values above that at which magnet 18 is effectively energized and within the limits of the apparatus.

I claim 1. A time limit controlling device for electric circuits, comprising a rotatable disk,

' current energized means for setting"up a driving torque therein, and means acting upon said disk movable toward and away from its periphery governed by the current energizing said driving means, to govern the rotation of said disk. I 2. A time limit controlling devicefor electric circuits, comprising a rotatable armature and current excited means for creating a driving torque therein, means for creating localized eddy currents in said rotatable armature, and means to vary the position of said localized eddy currents in proportion to a change in driving torque whereby to maintain substantially constant'effective driving torque.

3.\A time limit controlling device for electric circuits, comprising. a rotatable disk and ture and current excited means for creating a driving torque therein,'a magnet with its poles disposed on each side of the armature, and means controlledby the current of the torque producing means to vary the relative position of the poles of said magnet with respect to the armature to compensate for variations in driving torque.

, 5. time limit controlling device for electric circuits, comprising a rotatable armature and current excited. means for creating a driving torque therein, a magnet with its poles disposed on each side of the armature, and means controlled by the current of the torque producing means to vary the relative position of-the poles of said magnet with respect to the armature to compensate for variations in driving torque above a certain predetermined value.

6. A time limit controlling device for electric circuits, comprising a rotatable armature and current excited means for creating a driving torque therein, a magnet with its poles disposed on each side of the armature and means controlled by the current of the torque producing means to vary the position of the poles of the magnet vvlth respect to the periphery of said armature to compensate for variations in driving torque above a certain predetermined value.

In testimony whereof, I have signed my name to this specification, in the presence of two subscribing Witnesses.

GEORGE A. BURNHAM. Witnesses T. T. GREENWOOD, H. B. DAVIS. 

